Instead, it overturned two of its own prior decisions and struck down a key portion of the 2002 McCain-Feingold campaign-finance law. The effect of the ruling is that corporations and unions can now spend freely on political ads directly related to a candidate, and with no time restrictions.

Why did the Court take such a strong stand in support of the free speech rights of corporations? The answer is not that corporations, as legal “persons,” are necessarily entitled to the same rights as humans. They are obviously not. Dissolving a corporation is not murder, and regulating corporate speech does not silence a speaker about whom we have an obligation to care.

Instead, the Court focused on the real people who might hear the speech of corporations. “Speech is an essential mechanism of democracy,” Justice Kennedy wrote, “for it is the means to hold officials accountable to the people.” Hence, Kennedy seemed to suppose, more speech is always better for democracy.

But on reflection, the idea that more speech is always better should seem just as ridiculous as the idea that corporations should have equal moral standing with people. Speech is plainly bad for democracy if it misleads voters. It might even be bad if it affects views by repetition rather than persuasion, if it is simply so pervasive that it effectively drowns out competing voices.

The current political process is replete with examples of both kinds of speech. Exit polls after recent elections have shown that many voters hold false factual beliefs, and that these mistaken beliefs influence their votes. And the media blitz that saturates voters’ minds to the exclusion of all else is the goal of any campaign manager with enough money to pull it off. Under these circumstances, voters trying to inform themselves about the issues of the day are not shopping in a marketplace of ideas so much as looking for a needle in a haystack.

The reason that we are skeptical of government attempts to regulate political speech, then, is not that such speech is necessarily good. It is that people disagree about which speech is bad and fear that government officials with the power to make that call might use their power to protect themselves rather than enlighten the public.

But if we cannot identify low-value speech, can we at least identify low-value speakers? Corporations would seem to be pretty obvious candidates. One thing we should be able to agree on is that speech will generally seek to promote the interests of the speaker. That’s fine if the speaker is a person; the government should respond to the interests of the people.

But it should not respond to the interests of corporations, whose officers and directors are charged by law to enhance shareholder wealth rather than any abstract vision of the general good. If there is anything that is likely to lead systematically to worse governance, it is unrestricted corporate influence on the political process.

In the complicated world of the First Amendment, the line between corporations and people is one of the easiest to draw. Unfortunately, it is a line that the Court has just erased.

Why, again, would the Court do that? The decision makes sense if you assume that voters have a superhuman ability to resist the effects of pervasive and misleading political advertising. But that assumption is so obviously false that it is hard to believe it played much of a role in the ruling.

Instead, the justices in the majority seemed to be driven by the sincere fear that elected officials will suppress the vital truths that corporations are trying to tell us. That radical suspicion of government is what this decision comes down to.

The Supreme Court has told us that we should trust corporations more than our elected officials. Right or wrong, it is a sad comment on our democracy.